DEC 08 02RADIO TELESCOPE

Dane Coffey, Charles Wakefield, Stephanie Kaufman, Seung Hyun Song

Project Introduction and GoalDesign and develop a working Radio

Telescope that operates at the 1420 MHz frequency.

This is needed to give Astronomy and Physics students and faculty the ability to perform radio astronomy at Iowa State University

Telescope located at Fick ObservatorySponsored by the SSCL

Terminology

Celestial Coordinate SystemHorizontal Coordinate SystemRight Ascension and DeclinationAzimuth and Elevation

Concept Sketch

Parabolic Dish

Subreflector

Feedhorn

Coaxial Switch

Noise Source

Low Noise Amplifier

RF Mixer

Receiver

Limit Switches

Motors

Computer

Potentiometers

Stub Tuner

Motor Control

Attenuator

Web Server

Motor Control Interface

Attenuator Control

Coaxial Switch Control

User Interface Software

Internal Software

Limit Switch Detection

DAQ Card

Radio Source

Radio Waves

Coaxial Cable

Serial Cable

Outside Inside

Initial Situation

Ongoing since 1999Dish itself is assembled and motor’s are

functioningFail safe limit switches are installed and

functionReceiving system was purchased and

installedBasic software had been written

Software interface for controlling movement

Tracking software Raster Scan software

Initial Problems

Basic existing software is scattered and not cohesive

Position system is too inaccurate to even hit the sun

There is a lot of noise in the signal when performing raster scans

An attenuator was purchased but not functioning

The feed horn impendence is not matched

Debugging the receiver and front end is difficult

Initial Need

Create a single user interface with all critical software components

Create fully automatic position correction software and calibrate the current system

Improve S/N ratio by doing successive raster scans

Design attenuator control and develop software to control it

Design a single stub tuner to match the impedance

Create a simple two frequency signal generator for easy debugging of the system

Deliverables

Component Description

Unified user interface software

The unified software will be a LabVIEW program for users to easily interface with the telescope.

Pointing correction software

This LabVIEW software will be used to calibrate the telescope and generate offsets for more accurate telescope pointing.

Raster Scan Software The raster scan software will modified to do successive scans; this will be used to reduce the amount of noise in the image.

Feed Horn Circuitry Circuitry will be added to the feed horn to impedance match it with the coaxial cable.

Functioning Attenuator The attenuator will be installed and software will be modified to allow control the attenuator.

Signal Generator A two frequency signal generator will be created to easily debug the receiver and the front end.

Functional Requirements

Overall FR001: The system shall be capable of receiving,

amplifying, filtering, and capturing the intensity of incoming radio signals at a frequency of 1420 MHz.

Current FR008: The system shall have a single unified user

interface which incorporates all of the critical aspects needed for dish control and data collection including raster scan, manual control, tracking and intensity output features.

FR011: The unified software shall have a scheduler interface for users to set up complex daily data collection schedules.

Functional Requirements

Current Cont.FR017: The system shall have pointing

correction calibration software to automatically determine the offsets for elevation and azimuth.

FR018: The pointing correction software shall determine the offsets by scanning near known radio source locations.

FR022: The raster scan software shall perform successive scans to decrease the noise in the image.

FR024: The attenuator shall be capable of attenuating saturated signals with controllable gain of 0 to 15 dB.

Non-functional Requirements

OverallNFR002: The system software interface shall be

intuitive, and user friendly.NFR006: The positioning of the telescope shall

have an accuracy of within one-tenth of a degree.

CurrentNFR007: The impedance of the feed horn shall

be matched with the rest of the system as accurately as possible.

Operating Environment

Telescope outside at FickComponents indoors connected to

telescope~54 ° F indoors when not occupiedSoftware is written in LabVIEW and runs

on a Windows PCOutside temperatures from -20 ° F – 110

° FExposed to strong wind, rain, and snow

Risks and Risk Management

Weather – Take advantage of nice weather

Unforeseen problems – Be familiar with entire system

Knowledge passing – New teams need to involved as much as possible due to the large nature of the system

Design and Implementation

Impedance Match

Attenuator Control

Successive Raster Scan

Unified User Interface

Pointing Correction

Signal Generator

Parabolic Dish

Subreflector

Feedhorn

Coaxial Switch

Noise Source

Low Noise Amplifier

RF Mixer

Receiver

Limit Switches

Motors

Computer

Potentiometers

Stub Tuner

Motor Control

Attenuator

Web Server

Motor Control Interface

Attenuator Control

Coaxial Switch Control

User Interface Software

Internal Software

Limit Switch Detection

DAQ Card

Radio Source

Radio Waves

Coaxial Cable

Serial Cable

Outside Inside

Impedance Matching

System is 50 Ohm Feedhorn is 19.5 +

j19.7 at 1420 MHz Approximately 25% is

lost

Impedance Matching

Single stub designMicrostrip etched on copper clad glass epoxy

boardFeedhorn impedance measured at FickAssistance from Dr. Robert Weber

Impedance Matching

Tested using a model of the feedhornReturn loss is -30 dB at 1420 MHzMounted in Watertight Enclosure

Purpose of Attenuator

In the Spring of 06, the team was experiencing signal saturation when observing the Sun

In Fall of 06, the team bought the attenuator, JFW 15P-1499.

Purpose of Control Circuit

To match the voltage and current level Daq card digital I/O provide 0V low, 5V high Attenuator requires 0V low, 12V high Daq card has a very low current limit Attenuator requires 15mA of current for the

relay to switch

Attenuator Testing

Showed hysteresis characteristic Turn-on voltage: 8.5V Turn-off voltage: 3V

Insertion loss at 70MHz 0.6dB (65.3mV/70mV)

Attenuator Control

Eagle Schematic

Attenuator Control PCB Layout

Attenuator Control Testing Result

Attenuator Control Changes in DesignAddition of a buffer

To provide more current cushion 45mA from 25mA

Change from quad op amp to quad comparator To solve the voltage drop-off problem

Output voltage increased from 9.5V to 12V

Attenuator Control Considered DesignsOptocouplerOpen Collector Buffer

Attenuator Control Board

Raster Scan User Interface

Raster Scan Inputs

Raster Scan Outputs

Raster Scan Design/Implementation

Dish moves to Right Ascension and

Declination Coordinate

Intensity is read the number of times specified (making sure that the dish is in the correct place) by user and then averaged.

User Specifies:- Start and Stop Right Ascension- Start and Stop Declination- Right Ascension and Declination Step- Amount of Noise Reduction

Is there another

coordinate?

Graph of intensities is displayed and

output file is written.No

Yes

Raster Scan Testing

Noise Reduction = 1 Noise Reduction = 5

Maximum Intensity: 178Minimum Intensity: 143Difference: 35

Maximum Intensity: 158Minimum Intensity: 137Difference: 21

Pointing Correction and CalibrationTwo parts:Software to automatically determine the

minute offsets in the pointing to use for future measurements

Calibrating the current pointing system so that known sources can actually be hit

The software relies on the assumption that known sources can be hit

Pointing Correction SoftwareReads in a known source catalog and breaks up

the visible region into a grid scanning sources in each grid in both azimuth and elevation direction

Outputs offsets to text fileDesign: Scan

1 direction at a time Gaussian Fit Greedy Scheduling

Pointing Calibration

Feedback values are obtained by potentiometers attached to motors

Current algorithm and calibration method:

Azimuth limits switches are assumed at 0 and 360 degs

Elevation limits switches are assumed at 0 and 90 degs

Linear fit betweenProblems

Pointing Calibration

Similar process – scans of sun were taken, date/time and current feedback were recorded

Extrapolated limit switch locations

Does not pass sanity check Potentiometers are not linear enough?

Elevation Min Elevation Max Azimuth Min Azimuth Max-13.76208 83.58955 -41.15904 348.617172

Pointing Calibration

Motors swept at constant speed Obtained piecewise linear functions by combining with

previous results

Pointing Calibration

Problems Values change a lot with temperature

outside Conclusion

Accurate enough to hit the very large sun Current system is inadequate to hit any

other source Replace with digital shaft angle encoders

Unified User Interface

Single application to encompass all functionality for basic radio astronomy

Four sections were identified

Area Purpose

Real-Time Update A section of controls that continually polls the telescope to give real-time status updates. This includes current intensity, location in both celestial and horizontal systems, and limit switch status.

Telescope Power A single switch to turn the telescope on or off remotely.

Automatic Control Functionality that allows for the setting up of automatic scans of sources using a scheduler interface for time in the future.

Manual Control Functionality that allows for immediate movement of the telescope and immediate scans of sources.

Unified User Interface

Real-time update – Telescopes current status is continually polled

Telescope power - A single switch to turn on all components of the system

Unified User Interface

Automatic control – scheduler interface, outputs last scan results

Care was taken to ensure optimal interface for performing scans

Unified User Interface

Manual control – perform scans on the fly or position manually

Unified User Interface

Status: All functionality is implemented and tested Telescope power doesn’t function because of a

hardware issue that is being addressed by the new team

With a combination of our user interface and pointing calibration, blind scans of the sun can be performed easily, which has never been done before

Signal Generator

Two outputs: 70 MHz 1420 MHz

Switch only allows operation of one output at a time

PortableOperates on two 9-

volt batteries

Signal Generator

Signal Generator

Both outputs have been tested

70 Mhz signal stable when input is at least 13.5V

1420 MHz signal stable when input is at least 16V 1420 MHz signal is

acceptable when input is at least 15.5V

End of Semester Status and Future Issues were identified with the hardware that

turns the hardware components of the system on and off remotely

We’ve worked with the new team to fix this and they will be installing the new board

Once the potentiometers are replaced and the new system is calibrated the telescope will be ready for basic use with our new software

The same process and software used in calibration can be repeated to calibrate the shaft angle encoders

Mechanical problem with the shaft that rotates the azimuth potentiometer

Lessons Learned

A large system such as this requires frequent checks and maintenance that is hard to provide from senior design students

Not having immediate access to the system is a huge limitation

Minor setbacks dominate our time at the observatory

Documentation needs to be kept up to date with so many teams switching in and out

Cost Analysis

Budgeted Cost Scheduled (@ $10.00/hr)

Budgeted Cost Performance (@ $10.00/hr)

Actual Cost Performance (@ $10.00/hr)

Cost Variance

Schedule Variance

$8,800 $7,952 $8,485 0.94 .90Overall ended up slightly over budget, some things went quicker, others longer

Slightly below on scheduling, due to a few loose ends

There was quite a bit of variance in some of the actual/planned hours, but it averaged out

Conclusion

We accomplished all of the tasks we set out to do at the beginning of the project

Many of the topics covered were unfamiliar at the beginning of the semester, it was a great learning experience

The positioning is the one thing preventing the telescope from being used practically

Barring any major setbacks, we should be able to get astronomy students involved and using the telescope next semester

Acknowledgements

Our Advisor Dr. Basart The SSCL and Matt Nelson Dr. Weber

Questions?